/*

Copyright (c) 2010, 2012-2020, Arvid Norberg
Copyright (c) 2016-2017, Steven Siloti
Copyright (c) 2016-2018, Alden Torres
Copyright (c) 2017, Andrei Kurushin
All rights reserved.

You may use, distribute and modify this code under the terms of the BSD license,
see LICENSE file.
*/

#ifndef TORRENT_UTP_SOCKET_MANAGER_HPP_INCLUDED
#define TORRENT_UTP_SOCKET_MANAGER_HPP_INCLUDED

#include <map>
#include <functional>

#include "libtorrent/aux_/socket_type.hpp"
#include "libtorrent/session_status.hpp"
#include "libtorrent/enum_net.hpp"
#include "libtorrent/aux_/session_settings.hpp"
#include "libtorrent/span.hpp"
#include "libtorrent/aux_/packet_pool.hpp"

namespace libtorrent {

struct counters;

namespace aux {

	struct utp_stream;
	struct utp_socket_impl;

	// interface/handle to the underlying udp socket
	struct TORRENT_EXTRA_EXPORT utp_socket_interface
	{
		virtual udp::endpoint get_local_endpoint() = 0;
	protected:
		virtual ~utp_socket_interface() = default;
	};

	struct utp_socket_manager
	{
		using send_fun_t = std::function<void(std::weak_ptr<utp_socket_interface>
			, udp::endpoint const&
			, span<char const>
			, error_code&, udp_send_flags_t)>;

		using incoming_utp_callback_t =  std::function<void(aux::socket_type)>;

		utp_socket_manager(send_fun_t send_fun
			, incoming_utp_callback_t cb
			, io_context& ios
			, aux::session_settings const& sett
			, counters& cnt, void* ssl_context);
		~utp_socket_manager();

		// return false if this is not a uTP packet
		bool incoming_packet(std::weak_ptr<utp_socket_interface> socket
			, udp::endpoint const& ep, span<char const> p);

		// if the UDP socket failed with an EAGAIN or EWOULDBLOCK, this will be
		// called once the socket is writeable again
		void writable();

		// when the upper layer has drained the underlying UDP socket, this is
		// called, and uTP sockets will send their ACKs. This ensures ACKs at
		// least coalesce packets returned during the same wakeup
		void socket_drained();

		void tick(time_point now);

		void send_packet(std::weak_ptr<utp_socket_interface> sock, udp::endpoint const& ep
			, char const* p, int len
			, error_code& ec, udp_send_flags_t flags = {});
		void subscribe_writable(utp_socket_impl* s);

		void remove_udp_socket(std::weak_ptr<utp_socket_interface> sock);

		// internal, used by utp_stream
		void remove_socket(std::uint16_t id);

		utp_socket_impl* new_utp_socket(utp_stream* str);
		int gain_factor() const { return m_sett.get_int(settings_pack::utp_gain_factor); }
		int target_delay() const { return m_sett.get_int(settings_pack::utp_target_delay) * 1000; }
		int syn_resends() const { return m_sett.get_int(settings_pack::utp_syn_resends); }
		int fin_resends() const { return m_sett.get_int(settings_pack::utp_fin_resends); }
		int num_resends() const { return m_sett.get_int(settings_pack::utp_num_resends); }
		int connect_timeout() const { return m_sett.get_int(settings_pack::utp_connect_timeout); }
		int min_timeout() const { return m_sett.get_int(settings_pack::utp_min_timeout); }
		int loss_multiplier() const { return m_sett.get_int(settings_pack::utp_loss_multiplier); }
		int cwnd_reduce_timer() const { return m_sett.get_int(settings_pack::utp_cwnd_reduce_timer); }

		std::pair<int, int> mtu_for_dest(address const& addr);
		int num_sockets() const { return int(m_utp_sockets.size()); }

		void defer_ack(utp_socket_impl* s);
		void subscribe_drained(utp_socket_impl* s);

		void restrict_mtu(int const mtu)
		{
			m_restrict_mtu[std::size_t(m_mtu_idx)] = mtu;
			m_mtu_idx = (m_mtu_idx + 1) % int(m_restrict_mtu.size());
		}

		int restrict_mtu() const
		{
			return *std::max_element(m_restrict_mtu.begin(), m_restrict_mtu.end());
		}

		// used to keep stats of uTP events
		// the counter is the enum from ``counters``.
		void inc_stats_counter(int counter, int delta = 1);

		aux::packet_ptr acquire_packet(int const allocate) { return m_packet_pool.acquire(allocate); }
		void release_packet(aux::packet_ptr p) { m_packet_pool.release(std::move(p)); }
		void decay() { m_packet_pool.decay(); }

		// explicitly disallow assignment, to silence msvc warning
		utp_socket_manager& operator=(utp_socket_manager const&) = delete;

	private:

		send_fun_t m_send_fun;
		incoming_utp_callback_t m_cb;

		// replace with a hash-map
		using socket_map_t = std::multimap<std::uint16_t, std::unique_ptr<utp_socket_impl>>;
		socket_map_t m_utp_sockets;

		using socket_vector_t = std::vector<utp_socket_impl*>;

		// if this is set, it means this socket still needs to send an ACK. Once
		// we exit the loop processing packets, or switch to processing packets
		// for a different socket, issue the ACK packet and clear this.
		utp_socket_impl* m_deferred_ack = nullptr;

		// storage used for saving cpu time on "push_back"
		// by using already pre-allocated vector
		socket_vector_t m_temp_sockets;

		// sockets that have received or sent packets this
		// round, may subscribe to the event of draining the
		// UDP socket. At that point they may call the
		// user callback function to indicate bytes have been
		// sent or received.
		socket_vector_t m_drained_event;

		// list of sockets that received EWOULDBLOCK from the
		// underlying socket. They are notified when the socket
		// becomes writable again
		socket_vector_t m_stalled_sockets;

		// the last socket we received a packet on
		utp_socket_impl* m_last_socket = nullptr;

		int m_new_connection = -1;

		aux::session_settings const& m_sett;

		// stats counters
		counters& m_counters;

		io_context& m_ios;

		std::array<int, 3> m_restrict_mtu;
		int m_mtu_idx = 0;

		// this is  passed on to the instantiate connection
		// if this is non-nullptr it will create SSL connections over uTP
		void* m_ssl_context;

		aux::packet_pool m_packet_pool;
	};
}
}

#endif
